(a) Field of the invention:
The present invention relates to luminescent (light-emitting) diodes and more particularly it pertains to those luminescent diodes having at least one p-n hetero junction and a p-type substrate.
(b) Description of the prior art:
Some attempts have been made heretofore for the production of luminescent (light-emitting) diodes. For example, in U.S. Pat. No. 3,677,836 issued to M. R. Lorenz, there is disclosed a luminescent diode having a homo junction at which a p-region and an n-region have the same forbidden bandwidth, the forbidden bandwidths of the p-region and the n-region increasing with the distance from the junction. In this structure, the absorption of light emitted near the p-n homo junction is not avoidable. Though Lorenz further refers to a hetero junction formed in either the n-region or the p-region, he teaches that the hetero junction reflects backwardly the light emitted at a recombination region to take the light out again through the recombination region at the surface located remote from the hetero junction. U.S. Pat. No. 3,812,516 issued to Hayashi discloses an electroluminescent diode having both homo- and hetero-junctions and an n-type substrate. The hetero junction acts to give a carrier confinement effect and therefore a p-type region on that side of the hetero junction opposite to the homo junction has the widest band gap among those regions located in the vicinity of the junctions. This type of diode is still unsatisfactory in light-emitting performance. Hayashi does not disclose any working example with a double hetero (DH) junction and no homo junction, though Hayashi refers to a possibility of existence of such type of diode.